Catalytic manufacture of vinyl fluoride

ABSTRACT

This invention relates to a process for the production of vinyl fluoride by dehydrofluorination of 1,1-difluoroethane in the presence of a catalyst containing magnesium and/or zinc.

This application is a national filing under 35 USC 371 of InternationalApplication No. PCT/US97/20291 filed Nov. 10, 1997 and claims priorityof U.S. Provisional Application No. 60/031,092 filed Nov. 21, 1996.

FIELD OF THE INVENTION

This invention relates to processes for the production of vinylfluoride, and more particularly, to catalysts and to a catalytic processfor the dehydrofluorination of 1,1-difluoroethane to vinyl fluoride.

BACKGROUND

Vinyl fluoride is a useful monomer for the preparation of fluorocarbonpolymers which have excellent weathering and chemical resistanceproperties.

Vinyl fluoride can be produced from acetylene and hydrogen fluorideusing mercury catalysts. It can also be produced by thedehydrofluorination of 1,1-difluoroethane. The dehydrofluorination of1,1-difluoroethane to vinyl fluoride and hydrogen fluoride is anequilibrium reaction. According to published literature the followingequilibrium concentrations of vinyl fluoride (VF), based on the moles ofVF divided by the moles of HFC-152a +VF, have been determined; about 13%VF at 227° C., about 40% VF at 327° C. and about 99% VF at 427° C.

U.S. Pat. No. 2.599,631 discloses a process for the manufacture of vinylfluoride by the dehydrofluorination of HFC-152a The dehydrofluorinationis done in the presence or absence of a catalyst. Thedehydrofluorination catalysts disclosed include oxygen, charcoal, andthe free metals, salts and oxides of the elements of Groups IA, IB, IIA,IIB, VB and VIII of the periodic table. In an example using the divalentGroup II metal compound calcium fluoride as a catalyst (at about 500°C.), the conversion of HFC-1 52a to vinyl fluoride was 66% (i.e., about66% of equilibrium). There is an ongoing interest in developing moreefficient catalysts for the conversion of HFC- 152a to VF.

SUMMARY OF THE INVENTION

A process is provided for the manufacture of vinyl fluoride (i.e.,CH₂═CHF, VF or 1141) from 1,1-difluoroethane (i.e., CH₃CHF₂, F152a orHFC-152a) which comprises contacting said, 1,1-difluoroethane at anelevated temperature with a catalyst containing at least one divalentGroup II metal compound. The process of this invention is characterizedby contacting said 1,1-difluoroethane at a temperature of from about200° C. to 400° C. with a catalyst containing (a) at least one compoundselected from the oxides, fluorides and oxyfluorides of magnesium, zincand mixtures of magnesium and zinc, and optionally (b) at least onecompound selected from the oxides, fluorides and oxyfluorides ofaluminum; provided that the atomic ratio of any metals other thanmagnesium and zinc (e.g., aluminum) in total, to the total of magnesiumand zinc in said catalyst is about 1:4. or less (e.g., 1:9).

DETAILED DISCUSSION

The present invention provides a process for the manufacture of vinylfluoride by contacting 1,1-difluoroethane in the vapor phase in thepresence of catalysts selected from the group consisting of oxides,fluorides and oxyfluorides of magnesium, zinc and mixtures of magnesiumand zinc. The catalysts may also contain metals other than magnesiumand/or zinc provided that the atomic ratio of metals other thanmagnesium and zinc to the total of magnesium and zinc is about 1:4, orless. Of note are embodiments which contain in addition to the oxides,fluorides and/or oxyfluorides of magnesium and zinc, at least onecompound selected from the oxides, fluorides and oxyfluorides ofaluminum; provided that the atomic ratio of aluminum to the total ofmagnesium and zinc in said catalyst is about 1:4, or less (e.g., about1:9). Preferred catalysts include catalysts consisting essentially ofmagnesium fluoride, and catalysts consisting essentially of magnesiumfluoride and at least one compound selected from the oxides, fluoridesand oxyfluorides of aluminum.

A suitable catalyst may be prepared, for example, as follows:

Magnesium oxide is dried until essentially all water is removed, e.g.,for about 18 hours at about 100° C. The dried material is thentransferred to the reactor to be used. The temperature is then graduallyincreased to about 400° C. while maintaining a flow of nitrogen throughthe reactor to remove any remaining traces of moisture from themagnesium oxide and the reactor. The temperature is then lowered toabout 200° C. and a fluoriding agent such as HF or other vaporizablefluorine containing compounds such as SF₄, CCl₃F, CCl₂F₂, CHF₃ orCCl₂FCClF₂, diluted with nitrogen is passed through the reactor. Thenitrogen can be gradually reduced until only HF or other vaporizablefluorine containing compounds is being passed through the reactor. Atthis point the temperature can be increased to about 450° C. and held atthat temperature for a time sufficient (depending on the fluoridingagent flowrate and the catalyst volume) to convert the magnesium oxideto a fluoride content corresponding to at least 40% by weight (e.g., forfrom 15 to 300 minutes). The fluorides are in the form of magnesiumfluoride or magnesium oxyfluoride; the remainder of the catalyst ismagnesium oxide. It is understood in the art that fluoriding conditionssuch as time and temperature can be adjusted to provide higher than 40weight % fluoride-containing material.

Another suitable procedure for the catalyst preparation is to addammonium hydroxide to a solution of magnesium nitrate and (if present)zinc nitrate and/or aluminum nitrate. The ammonium hydroxide is added tothe nitrate solution to a pH of about 8.8. At the end of the addition,the solution is filtered, the solid obtained is washed with water, driedand slowly heated to 500° C., where it is calcined. The calcined productis then treated with a suitable fluorine-containing compound asdescribed above.

The physical shape of the catalyst is not critical and may, for example,include pellets, powders or granules. Although not necessary, catalystswhich have not been fluorided can be treated with HF before use. It isthought that this converts some of the surface oxides to oxyfluorides.This pretreatment can be accomplished by placing the catalyst in asuitable container (which can be the reactor to be used to perform thereaction of the instant invention) and thereafter, passing HF over thedried catalyst so as to partially saturate the catalyst with HF. This isconveniently carried out by passing HF over the catalyst for a period oftime (e.g., about 15 to 300 minutes) at a temperature of, for example,about 200° C. to about 450° C. Nevertheless, this HF treatment is notessential.

The reaction temperature will normally be within the range from about200° C. to about 400° C., preferably about 225° C. to 375° C. To providefor low acetylene by-product formation and to enhance catalyst life, thetemperature is preferably kept within the range of from about 250° C. toabout 300° C., more preferably, from about 250° C. to about 280° C.

The 1,1-difluoroethane is typically passed over the catalyst at a rateof about 60 volumes to about 3600 volumes per volume of catalyst perhour; preferably 120 volumes to 720 volumes per volume of catalyst perhour. These volumes correspond to a contact time of about 60 seconds toabout 1 second and preferably about 30 seconds to about 5 seconds.Normally a contact time is employed which is sufficient to provide adehydrofluorination of HFC- 152a equal to at least 50% of theequilibrium value for conversion of 1,1-difluoroethane to vinyl fluorideat the temperature employed; preferably at least 80%, and morepreferably at least 90% of the equilibrium value at a given reactiontemperature.

The reaction pressure can be subatmospheric, atmospheric orsuperatmospheric. Generally, near atmospheric pressures are preferred.

Unreacted starting material can be recycled to the reactor for theproduction of additional CH₂═CHF. Vinyl fluoride (b.p. −72° C.) may berecovered from the reaction product and any unreacted 1,1-difluoroethane(b.p. −25° C.) by conventional procedures such as distillation.

The process of this invention can be carried out readily in the vaporphase using well known chemical engineering practice.

The reaction zone and its associated feed lines, effluent lines andassociated units should be constructed of materials resistant tohydrogen fluoride. Typical materials of construction, well-known to thefluorination art, include stainless steels, in particular of theaustenitic type, the well-known high nickel alloys, such as Monel®nickel-copper alloys, Hastelloy® nickel-based alloys and, Inconel®nickel-chromium alloys, and copper-clad steel. Silicon carbide is alsosuitable for reactor fabrication.

Without further elaboration, it is believed that one skilled in the artcan, using the description herein, utilize the present invention to itsfullest extent. The following specific embodiments are to be construedas illustrative, and not as constraining the remainder of the disclosurein any way whatsoever.

EXAMPLES

Legend 1141 is CH₂═CHF GCMS is gas chromatography- F152a is CH₃CHF₂ massspectroscopy CT is contact time k_(f) is rate constant of the k_(r) israte constant of forward reaction the reverse reaction

PREPARATION OF CATALYSTS

General Procedure for the Preparation of Metal Fluoride Catalysts:

Unless stated otherwise, the following general procedure was followedfor the preparation of metal fluoride catalysts containing one or moremetal fluorides. An aqueous solution of the metal(s) halide(s) ornitrate(s) in deionized water was treated with 48% aqueous HF withstirring. Stirring was continued overnight and the slurry evaporated todryness on a steam bath. The dried solid was then calcined in air at400° C. for about four hours, cooled to room temperature, crushed andsieved to provide a 12-20 mesh (1.68-0.84 mm) fraction which was used incatalyst evaluations.

Preparation of MgF₂ Catalyst:

Following the general procedure described above for the preparation offluorinated catalysts, a MgF₂ catalyst was prepared from 150.0 g ofMg(NO₃)₂.6H₂O, 500 mL deionized water and 75 mL 48% aqueous HF.

Preparation of MgF₂/AlF₃ (98:2):

Following the general procedure described above for the preparation offluorinated catalysts, a MgF₂/AlF₃ catalyst having a nominal magnesiumto aluminum atomic ratio of 43:1 was prepared from 251.28 gMg(NO₃)₂.6H₂O, 7.50 g Al(NO₃)₃.9H₂O and 100 mL 48% aqueous HF.

Preparation of MgF₂/AlF₃ (9:1):

Following the general procedure described above for the preparation offluorinated catalysts, a MgF₂/AlF₃ catalyst having a nominal magnesiumto aluminum atomic ratio of 9:1 was prepared from 237.6 g Mg(NO₃)₂.6H₂O,34.76 g Al(NO₃)₃.9H₂O and 120 mL 48% aqueous HF.

Preparation of MgF₂/AlF₃ (1:1):

Following the general procedure described above for the preparation offluorinated catalysts, a MgF₂/AlF₃ catalyst having a nominal magnesiumto aluminum atomic ratio of 1:1.1 was prepared from 128.2 gMg(NO₃)₂.6H₂O, 187.56 g Al(NO₃)₃.9H₂O and 120 mL 48% aqueous HF.

Preparation of MgF₂/AlF₃ (1:9):

Following the general procedure described above for the preparation offluorinated catalysts, a MgF₂/AlF₃ catalyst having a nominal magnesiumto aluminum atomic ratio of 1:11 was prepared from 23.07 gMg(NO₃)₂.6H₂O, 337.6 g Al(NO₃)₃.9H₂O and 166 ml 48% aqueous HF.

Preparation of ZnF₂:

Following the general procedure described for the preparation offluorinated catalysts, ZnF₂ was prepared from an aqueous solution of148.73 g of Zn(NO₃)₂.6H₂O and 62 mL of 48% aqueous HF.

Preparation of ZnF₂/AlF₃ (1:1):

Following the general procedure described for the preparation offluorinated catalysts, a ZnF₂/AlF₃ catalyst having a nominal zinc toaluminum atomic ratio of 2.4:1 was prepared from 148.73 g Zn(NO₃)₂.6H₂O,187.56 g Al(NO₃)₃.9H₂O and 150 mL 48% aqueous HF.

Preparation of ZnF₂/AlF₃ (1:9):

Following the general procedure described for the preparation offluorinated catalysts a ZnF₂/AlF₃ catalyst having a nominal zinc toaluminum atomic ratio of 0.2:1 was prepared from 26.77 g Zn(NO₃)₂.6H₂O,337.6 g Al(NO₃)₃.9H₂O and 166 mL 48% aqueous HF.

Preparation of ZnF₂/AlF₃ (9:1):

Following the general procedure described for the preparation offluorinated catalysts, a ZnF₂/AlF₃ catalyst having a nominal zinc toaluminum atomic ratio of 24:1 was prepared from 267.71 g Zn(NO₃)₂.6H₂O,33.76 g Al(NO₃)₃.9H₂O and 120 mL 48% aqueous HF.

Preparation of Fluorided Magnesium Oxide

To a reactor was charged 5.42 g, 5 cc of a commercial sample ofmagnesium oxide which was granulated to {fraction (12/20)} mesh(1.68/0.84 mm) prior to use. It was heated in a flow of nitrogen (50cc/min) for about one hour at 175° C. After this period, a flow of HF(50 cc/min) was started through the reactor. The reactor was maintainedfor an additional hour at 175° C. After this period, the nitrogen flowwas reduced to 20 cc/min and the HF flow increased to 80 cc/min. Thereactor temperature was then gradually raised to 400° C. over a two hourperiod. The reactor contents were cooled to room temperature under aflow of nitrogen. When discharged, the fluorinated catalyst weighed 6.6g which corresponds to a 40% conversion of MgO to MgF₂.

Magnesium oxide, gamma- alumina, calcium fluoride and alpha andbeta-aluminum fluorides were obtained from commercial sources as powdersand were granulated prior to use.

Examples 1 to 9

This series of examples demonstrates catalyst efficacy for thedehydrofluorination of 1,1-difluoroethane (HFC-152a) to vinyl fluoride(1141).

Table 1 (Examples 1 to 9) shows three specific catalysts, each studiedin three different reactors: one to determine the rate of reaction, onefor catalyst life, and one for coproduct formation.

TABLE 1 First Reactor Second Reactor Third Reactor Example ExampleExample Example k_(f)(sec)⁻¹ Hours (cat. % 1141 % acetylene Catalyst275° C. life) 275° C. 275° C. 260° C. MgF₂ 1 2 2 3 0.26 550 30 0.000MgF₂/AlF₃ 4 5 5 6 (98:2) 1.00 511 33 0.014 MgF₂/AlF₃ 7 8 8 9 (9:1) 1.18723 40 0.069 CT(sec)-> .055-.79 6 6 6

The reactor used to collect the data in Examples 1, 4, and 7 consistedof a 6″ (15.2 cm)×¼″ (0.64 cm) stainless steel tube. It was heated in afurnace to internal reactor temperatures of 225, 250, and 275° C. Therates of reaction were determined by measuring the percent conversion asa function of contact time; the actual flows of F152a were 10 (1.7×10⁻⁷m³/s), 25 (4.2×10⁻⁷ m³/s), 38 (6.3×10⁻⁷ m³/s), 50 (8.3×10⁻⁷ m³/s), 75(1.3×10⁻⁶ m³/s), 100 (1.7×10⁻⁶ m³/s), and 144 (2.4×10⁻⁶ m³/s) sccm. Thevolume of catalyst used in all cases was 0.132 mL ground to 20-25 mesh(0.84-0.71 mm) and dried by heating at 250° C. for 1 hour while purgingwith dry nitrogen flowing at 25 sccm(4.2×10⁻⁷ m³/s). The rate of thedehydrofluorination was determined by fitting the data to the followingset of equations,

CH₃CHF₂→CH₂═CHF+HF   k_(f)

CH₂═CHF+HF →CH₃CHF₂   k_(r)

while monitoring the HFC-152a and vinyl fluoride concentrations at theconditions mentioned above.

The data in Examples 2, 5 and 8 were determined in a ½″ (1.3 cm)×11″(27.9 cm) tubular reactor made of Hastelloy™ nickel alloy. The catalystswere dried by heating to 350° C. for 16 hours under a flow of drynitrogen of 50 sccm (8.3×10⁻⁷ m³/s) prior to actual use. The reactor wascooled to 275° C. and a flow of F152a was begun at 50 sccm (8.3×10⁻⁷m³/s). When the flow of vinyl fluoride began to decrease from itsnear-equilibrium value, the run was concluded. All of the catalysts wereground to 12×20 mesh (1.68-0.84 mm).

The reactor used for the data in Examples 3, 6 and 9 was an Inconel™nickel alloy ¾″ (1.9 cm)×12″ (30.5 cm) pipe with an internal diameter of⅝″ (1.6 cm). The catalysts (5 mL) were dried by heating to 260° C. undera flow of dry nitrogen of 50 sccm (8.3×10⁻⁷ m³/s) prior to use. A flowof F152a was begun at 50 sccm (8.3×10⁻⁷ m³/s). The reactor products weresampled every hour, and the products were determined by GCMS. All of thecatalysts were ground to 12×20 mesh (1.68-0.84 mm).

Comparative Example A

Calcium fluoride (5.6 gm, 5.0 mL, 12-20 mesh (1.68-0.84 mm)) was placedin an Inconel™ nickel alloy ¾″ (1.9 cm)×12″ (30.5 cm) pipe with aninternal diameter of ⅝″ (1.6 cm). The catalyst was dried by heating to250° C. under a flow of dry nitrogen of 50 sccm (8.3×10⁻⁷ m³/s) prior touse. HFC-152a was passed into the reactor at 50 sccm (8.3×10⁻⁷ m³/s)at260 and 275° C. The results are shown in Table A.

TABLE A Temp(° C.) % F152a % 1141 260 99.5 0.5 275 99.8 0.8

Example 10

Magnesium oxide (5.4 gm, 5 cc, 12-20 mesh (1.68-0.84 mm)) was placed inan Inconel™ nickel alloy ¾″ (1.9 cm)×12″ (30.5 cm) pipe with an internaldiameter of ⅝″ (1.6 cm). The catalyst was dried by heating to 260° C.under a flow of dry nitrogen of 50 sccm (8.3×10⁻⁷ m³s) prior to use, andactivated by treating with a flow of HF up to 80 sccm (1.3×10⁻⁶ m³/s)and up to 400° C. A flow of F152a was begun at 50 sccm (8.3×10⁻⁷ m³/s).The contact time was 12 seconds. The reactor products were sampled everyhour, and the products were determined by GCMS. The results are shown inTable 2.

TABLE 2 Temp(° C.) % F152a % 1141 260 76.0 24.0

Example 11

ZnF₂ (1 mL, 12-20 mesh (1.68-0.84 mm)) was placed in a ¼″ (0.64 cm)×3″(7.6 cm) tubular Hastelloy™ nickel alloy reactor. The reactor was heatedto 275° C. and a flow of F152a was begun at 5 sccm (1.7×10⁻⁷ m³/s) togive a contact time of 12 sec. The results are shown in Table 3.

TABLE 3 Temp(° C.) % F152a % 1141 275 90 10

Example 12

ZnF₂/AlF₃ (9:1, 0.132 mL, 20-25 mesh (0.84 to 0.71 mm)) was placed in a6″ (15.2 cm)×¼″ (0.64 cm) stainless steel tube heated in a furnace andwas dried by heating at 250° C. for 1 hour while purging with drynitrogen flowing at 25 sccm (4.2×10⁻⁷ m³/s). The temperature was thenraised to 275° C. and F152a was passed over the catalyst at 25 sccm(4.2×10⁻⁷ m³/s). The contact time was 0.32 seconds. The conversion ofF152a was monitored by gas chromatography; the %1141 was 15.

Comparative Examples B-H

The reactor was the same as that of Example 11 for Comparative ExampleB. ZnF₂/AlF₃ (1:9) (1 mL, 12-20 mesh (1.68-0.84 mm)) was heated to 275°C. and a flow of F152a was begun at 20 sccm (1.7×10⁻⁷ m³/s) to give acontact time of 3 sec. The results are shown in Table B. For the rest ofthe comparative examples, the catalyst was placed in a 6″ (15.2 cm)×¼″(0.64 cm) stainless steel tube heated in a furnace (0.132 mL, 20-25 mesh(0.84 to 0.71 mm)) and was dried by heating at 250° C. for 1 hour whilepurging with dry nitrogen flowing at 25 sccm (4.2×10⁻⁷ m³/s). Thetemperature was then raised to 275° C. and F152a was passed over thecatalyst at 25 sccm (4.2×10⁻⁷ m³/s). The contact time was 0.32 seconds.The conversion of F152a was monitored by gas chromatography; the resultsare shown in Table B.

TABLE B Example Catalyst % 1141 B ZnF₂/AlF₃ 24 (1:9) C MgF₂/AlF₃ 27(1:9) D gamma-Al₂O₃ 28 E ZnF₂/AlF₃ 22 (1:1) F MgF₂/AlF₃ 30 (1:1) Galpha-AlF₃ 22 H beta-AlF₃ 12

What is claimed is:
 1. A process for the manufacture of vinyl fluoridefrom 1,1-difluoroethane which comprises contacting said1,1-difluoroethane at an elevated temperature with a catalyst containingat least one divalent Group II metal compound, characterized by:contacting said 1,1-difluoroethane at a temperature of from about 200°C. to 400° C. with a catalyst containing (a) at least one compoundselected from the oxides, fluorides and oxyfluorides of magnesium, zincand mixtures of magnesium and zinc, and optionally (b) at least onecompound selected from the oxides, fluorides and oxyfluorides ofaluminum; provided that the atomic ratio of any metals other thanmagnesium and zinc, in total, to the total of magnesium and zinc in saidcatalyst is about 1:4, or less.
 2. The process of claim 1 wherein acontact time is employed which is sufficient to provide adehydrofluorination of 1,1-difluoroethane equal to at least 80% of theequilibrium value for conversion of 1,1-difluoroethane to vinyl fluorideat the temperature employed.
 3. The process of claim 2 wherein thetemperature is from 250° C. to 280° C.
 4. The process of claim 3 whereinthe catalyst consists essentially of magnesium fluoride.
 5. The processof claim 3 wherein the catalyst consists essentially of magnesiumfluoride and at least one compound selected from the oxides, fluoridesand oxyfluorides of aluminum.
 6. The process of claim 1 wherein thecatalyst contains at least one compound selected from the oxides,fluorides, and oxyfluorides of aluminum.
 7. The process of claim 6wherein the atomic ratio of aluminum to the total of magnesium and zincis about 1:9.
 8. The process of claim 7 wherein the catalyst consistsessentially of magnesium fluoride and at least one compound selectedfrom the oxides, fluorides and oxyfluorides of aluminum.
 9. The processof claim 1 wherein the catalyst consists essentially of magnesiumfluoride.
 10. The process of claim 1 wherein the catalyst consistsessentially of magnesium fluoride and at least one compound selectedfrom the oxides, fluorides and oxyfluorides of aluminum.
 11. A processorthe manufacture of vinyl fluoride from 1,1-difluoroethane whichcomprises contacting said 1,1-difluoroethane at an elevated temperaturewith a catalyst containing at least one divalent Group II metalcompound, characterized by: (1) said 1,1-difluoroethane being contactedwith said catalyst at a temperature of from about 200° C. to 400° C.;(2) said at least one divalent Group II metal compound being selectedfrom the oxides, fluorides and oxyfluorides of magnesium; and (3) saidcatalyst further containing at least one compound selected from theoxides, fluorides and oxyfluorides of aluminum; provided that the atomicratio of any metals other than magnesium, in total, to the totalmagnesium in said catalyst is about 1:4, or less.
 12. The process ofclaim 11 wherein said catalyst consists essentially of magnesiumfluoride and aluminum fluoride; and wherein said catalyst contact issufficient to provide a dehydrofluorination of 1,1-difluoroethane tovinyl fluoride of at least 80% of the equilibrium value at the reactiontemperature.
 13. A process for the manufacture of vinyl fluoride from1,1-difluoroethane which comprises contacting said 1,1-difluoroethane atan elevated temperature with a catalyst containing at least one divalentGroup II metal compound, characterized by: (1) said 1,1-difluoroethanebeing contacted with said catalyst at a temperature of from about 200°C. to 400° C.; (2) said at least one divalent Group II metal compoundbeing selected from the oxides, fluorides and oxyfluorides of magnesium;and (3) the atomic ratio of any metals other than magnesium, in total,to the total magnesium in said catalyst being about 1:4, or less. 14.The process of claim 13 wherein said catalyst consists essentially ofmagnesium fluoride; and wherein said catalyst contact is sufficient toprovide a dehydrofluorination of 1,1-difluoroethane to vinyl fluoride ofat least 80% of the equilibrium value at the reaction temperature.